A class of machines exists in the art generally known as "scroll" machines which are used for the displacement of various types of fluids. Such machines may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor.
Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration, each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180 degrees from the other. The machine operates by orbiting one scroll member (the orbiting scroll) with respect to the other scroll member (the non-orbiting scroll) to produce moving line contacts between the flanks of the respective wraps. These moving line contacts define moving isolated crescent-shaped pockets of fluid. The spiral scroll wraps are commonly formed as involutes of a circle. Ideally, there is no relative rotation between the scroll members during operation, the motion is purely curvilinear translation (no rotation of any line of the body). The relative rotation between the scroll members is typically prohibited by the use of an Oldham coupling.
The moving fluid pockets carry the fluid to be handled from a first zone in the scroll machine where a fluid inlet is provided, to a second zone in the scroll machine where a fluid outlet is provided. The volume of the sealed pocket changes as it moves from the first zone to the second zone. At any one instant of time, there will be at least one pair of sealed pockets, and when there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally within the machine, the first zone being located at the outer periphery of the apparatus.
The Oldham coupling that prohibits the relative rotation between the scroll members has taken various forms but generally incorporate two pairs of keys projecting from an annular ring. One pair of keys engages slots in the orbiting scroll and the other pair of keys engages slots in the non-orbiting scroll member or a stationary body such as a bearing housing.
While such Oldham couplings which are connected between the two scroll members are effective to prevent rotation between these respective scroll members, they present design and/or assembly problems in regards to positioning of the coupling between the scroll members. Alternatively, in other applications, additional support structure and/or increased shell size may be required to support the Oldham coupling radially outwardly of the scroll members.
The present invention, in one embodiment, provides an Oldham coupling which is capable of directly interconnecting the two scroll members so as to effectively prevent relative rotation therebetween while avoiding potential design problems presented by the prior designs and also reducing the number of locating and positioning surfaces required. The present invention provides an Oldham coupling which has only one pair of posts for engagement with the scroll members. The orbiting scroll member contacts the lower portion of the pair of keys and the non-orbiting scroll member contacts the upper portion of the pair of keys. In one embodiment the single pair of keys is attached to an annular ring and in another embodiment the single pair of keys is attached to an arc segment of an annular ring extending between the keys.
In an additional embodiment of the present invention an Oldham coupling directly interconnects the orbiting scroll member with the main bearing housing to prevent rotation of the orbiting scroll member. This Oldham coupling also has a single pair of keys for engagement with the orbiting scroll member and the main bearing housing. The single pair of keys can be connected to an annular ring or they can be connected to an arc segment of an annular ring.